The invention pertains to the field of analysis of chromatograms to determine the identity and composition of the components in liquid and gas compositions. More particularly, the invention relates to the use of known cross-correlation and moment analysis techniques to analyze chromatograms.
It is useful in the chemical analysis arts to be able to identify the individual components in a solution or a gas and the concentration of each component. For example, if groundwater is found to be polluted with gasoline, a chromatogram of the gasoline can be taken and compared to chromatograms of gasoline samples taken from service stations, oil refineries, pipelines and petroleum facilities in the area that could have contributed the pollution. In the past, such analysis was done by hand by injecting the unknown solution into a chromatography column and detecting the various components in the effluent output stream in a known fashion. The detector output was then converted into a chromatogram. Then samples from the known solutions were then injected into the chromatography column and various chromatograms were developed, one for each known solution. Then the chromatogram for the unknown sample is compared to the chromatograms of the known samples by hand to determine the source of the pollution. This has been done in the past by placing the chromatograms one on top of the other on a light table and comparing the chromatograms peak for peak. Obviously, this is a laborious, time consuming and expensive process.
Therefore, a need has arisen for a computerized method and apparatus where chromatograms from various sources can be compared automatically to generate some indication of the degree of similarity or difference.
Cross-correlation analysis is well-known in the arts, and has for many years been used in signal processing. Cross-correlation is a mathematical method of comparing one signal wave form or function to another to determine the degree of similarity. If a high degree of similarity exists, a very large peak will be observed in the cross correlation function at the moment in time when the two waveforms or functions being compared overlap each other to the greatest extent. In the prior art, cross correlation analysis has been used in the field of spectroscopy to compare spectra of excitation-emission matrices. Such a methodology was described in a paper by T. M. Rossi and I. M. Warner entitled "Pattern Recognition of Two-dimensional Florescence Data Using Cross-Correlation Analysis", Volume 39, Number 6, 1985 of Applied Spectroscopy, at page 949. To date however, no cross-correlation analysis has ever been performed by computer on chromatograms.